GENETICS TEST II - Daytona State College

Transcription

GENETICS
TEST II
REVIEW
The Academic Support Center @ Daytona State College (Science 102, Page 1 of 47)
BE ABLE TO DEFINE
• Linkage
•
The condition in which genes are present on the same chromosome, causing them to be
inherited as a unit, provided that they are not separated by crossing over during meiosis.
• Complete Linkage
•
A condition in which two genes are located so close to each that no recombination occurs
between them.
• Unlinked
•
Condition in which two genes are located so far apart that recombination occurs.
•
The independent behavior of each pair of homologous chromosomes during their segregation
in meiosis I. The random distribution of maternal and paternal homologs into their gametes.
• Independent Assortment
• Recombination
•
•
•
The process that leads to the formation of new allele combinations on chromosomes.
The reshuffling of alleles between homologs.
Increases genetic variation during meiosis I. Two types of recombination.
•
•
Crossing over – exchange of DNA between homologous chromosomes.
Random separation – (assortment/segregation) of homologous chromosomes.
•
•
•
Independent assortment – orientation of homologous pairs to poles is random.
All possible combinations of gametes should be formed in equal frequency
Formula for number of combinations is 2n
• Interlocus distance
•
•
The distance between any two loci on a single chromosome.
The interlocus distance is proportional to the frequency of crossing over between any two loci
on a single chromosome.
BE ABLE TO DEFINE
• Centimorgan or map unit
• One map unit (mu) or centimorgan (cM) is defined as 1 percent recombination
between two genes on a chromosome. Centimorgans are relative distances not exact
distances.
• Crossover
• A single crossover (SCO) alters linkage between two genes only if the crossover occurs
between those two genes.
• Chiasma
• Synapsed homologous chromosomes, in meiosis, wrap around each other, creating
chaismata, which are X-shaped intersections that are points of genetic exchange.
• Somatic cell hybridization
• The fusion of two cells to forma a single hybrid cell, called a heterokaryon.
• Heterokaryon
• A somatic cell containing nuclei from two different sources.
• Synkaryon
• The fusion of two gametic or somatic nuclei.
• In somatic cell genetics, the product of nuclear fusion.
• Upon continue culturing of a heterokaryon, chromosomes from one of the two parental
species are gradually lost until only a few chromosomes of one species remain and
most chromosomes are from the other species, creating what is termed a synkaryon.
BE ABLE TO DEFINE
• Synteny testing
• In somatic cell genetics, a method for determining whether two genes are
on the same chromosome.
• A panel of cell lines, each containing just a few human chromosomes, can
used for synteny testing in which the presence or absence of a specific gene
product is correlated with the presence or absence of each chromosome.
• Adaptation Hypothesis
• Proposes that the interaction of the bacteriophage and bacterium is
essential to the bacterium’s acquisition of immunity to the phage.
• Spontaneous Mutation
• A mutation that is not induced by a mutagenic agent.
• Spontaneous mutation that occurs in the presence or absence of phage is
considered the primary source of genetic variation in bacteria.
• Luria-Delbruck Experiment
• Proved that spontaneous mutation occurs prior to exposure to selective
agent.
• Referred to as the fluctuation test.
• Example - 100 tubes grown
• Many have zero mutants
• Few mutant colonies – cells had a mutation late in cell culture growth
• Few have lots of mutant colonies – mutation occurred early in cell culture growth.
BE ABLE TO DEFINE
• Prototroph
• A prototroph can synthesize all essential organic compounds, and therefore can be
grown on minimal medium.
• A strain usually of a microorganism that is capable of growth on a defined, minimal
medium. Wild-type strains are usually regarded as prototrophs and contrasted with
auxotrophs.
• Auxotroph
• Through mutation, an auxotroph has lost the ability to synthesize one or more essential
compounds, and must be provided with them in the medium if it is it grow.
• A mutant microorganism or cell line that requires a nutritional substance for growth that
can be synthesized and is not required by the wild-type strain.
• Conjugation
• Temporary fusion of two single-celled organisms for the sexual transfer of genetic
material.
• Bacteria undergo conjugation, in which:
•
•
Genetic information from one bacterium is transferred to another.
It recombines with the second bacterium’s DNA
• Fertility Factor
• An episomal plasmid in bacterial cells that confers the ability to act as a donor in
conjugation.
•
•
•
F+ cell : A bacteria cell that contains a fertility factor and acts as a donor in bacterial
conjugation
F- cell : A bacteria cell that does not contain a fertility factor and acts a recipient in
bacterial conjugation.
F- cells become F+ cells after conjugation.
BE ABLE TO DEFINE
• Merozygote
• A partially diploid bacteria cell containing, in addition to its own
chromosome, a chromosome fragment introduced into the cell by
transformation, transduction, or conjugation.
• Plasmids
• Extrachromosomal, circular DNA molecule that replicates independently of
the host chromosome.
• Contain one or more genes and replicate independently of the bacteria
chromosome.
• Three types to know
• Hfr
•
•
•
F Factors – confer fertility
R plasmids – confer antibiotic resistance
Col plasmids – encode colicins that can kill neighboring bacteria
• High-frequency recombination
• An Hfr strain has the F factor intergrated into its chromosome.
• An Hfr strain can donate genetic information to an F- cell, but the recipient
does not become F+
• F+ x F-  Recipient becomes F+ : Low rate of recombination
• Hfr x F-  Recipient remains F- : High rate of recombination
BE ABLE TO DEFINE
• Lysogeny
• The process by which the DNA of an infecting phage becomes repressed
and integrated into the chromosome of the bacterial cell it infects.
• Lysogency occurs when:
• The phage DNA integrates into the bacterial chromosome.
• It is replicated along with the chromosome.
• It is passed to daughter cells
• Lysogenic
• When a bacteria cell carries the DNA of a temperate bacteriophage
integrated into its chromosome.
• Bacteria containing a prophage are lysogenic and can grow and divide
stably until viral reproduction is induced.
• Prophage
• A bacteriophage genome integrated into a bacterial chromosome that is
replicated along with the bacterial chromosme.
• Plaque
• On an otherwise opaque bacteria lawn, a clear area caused by the growth
and reproduction of a single bateriophage.
• Areas clear of bacteria on a plate which can be counted to determine the
number of phages in the original culture.
BE ABLE TO DEFINE
• Transduction
• Virus-mediated bacteria DNA transfer
• Virally mediated bacterial recombination. Also used to describe
the transfer of eukaryotic genes mediated by a retrovirus.
• Generalized Transduction
• The transfer of any gene from bacterial host to a bacterial
recipient in a process mediated by a bacteriophage.
• In generalized transduction bacterial DNA instead of phage
DNA is packaged in a phage particle and transferred to a host.
• Generalized transduction results in transfer of a large number of
bacterial genes.
• Specialized Transduction
• Genetic transfer of specific host genes by transducing phages.
• In specialized transduction, a small piece of bacterial DNA is
packaged along with the phage DNA.
• Specialized transduction results in transfer of only a few bacterial
genes.
BE ABLE TO DEFINE
• Transformation
•
•
In transformation, small pieces of extracellular DNA are taken up by a living bacterial cell and
integrated stably into the chromosome.
Heritable change in a cell or an organism bought about by exogenous DNA. Known to occur
naturally and also used in recombinant DNA studies.
• Cotransformation
•
•
Genes that are close enough to each other to be cotransformed are linked.
When two or more genes are integrated together into a cell.
•
Interrupted matings demonstrated that specific genes in an Hfr strain are transferred and
recombined sooner than others.
Experimention by Wollman & Jacob that explained the difference between Hfr cells and F+
cells and showed how Hfr strains would allow genetic mapping of the E. Coli chromosome.
• Interrupted mating technique
•
INTERRUPTED MATINGS
• Interrupted matings demonstrated that specific
genes in an Hfr strain are transferred and
recombined sooner than others
• The chromosome of an Hfr strain is transferred
linearly.
• Gene transfer by Hfr strains led to the
understanding that the E. coli chromosome is
circular
• The origin is determined by the point of
integration of the F factor into the chromosome,
and direction of transfer is determined by the
orientation of F factor integration.
BE ABLE TO DEFINE
• Heteroduplex
• A double-stranded nucleic acid molecule in which each
polynucleotide chain has a different origin. It may be produced
as an intermediate in a recombinational event or by the in vitro
reannealing of single-stranded, complementary molecules.
• In transformation, once the extracellular DNA is integrated into
the chromosome, the recombinant region contains one host
strand and one mutant strand. This region is referred to as a
heteroduplex.
• Bacteriophage
• Bacterial viruses.
• A virus that infects bacteria, using it as the host for reproduction.
• Sex chromosomes
• Dissimilar, or heteromophic chromosomes such as the XY pair in
mammals, characterize one sex or the other in a wide range of
species, resulting in their label as sex chromosomes.
BE ABLE TO DEFINE
• XX/XO
• The mode of determination used by the Protenor (butterfly)
and some other insects.
• Depends on the random distribution of the X chromosome
into half of the male gametes.
• The presence of two X chromsomes (XX) in the zygote results
in female offspring.
• The presence of one X chromsome (XO) results in male
offspring
BE ABLE TO DEFINE
• ZZ/ZW
• The mode of determination used by most birds and some
moths/butterflies, fish, reptiles, and amphibians.
• The presence of one Z chromsome and one W chromosome
(ZW) results in female offspring. (heterogametic)
• The presence of two X chromsomes (ZZ) in the zygote results
in male offspring (homogametic).
• All male gametes have an Z chromosome, female gametes
have either Z or W.
BE ABLE TO DEFINE
• XX/XY
• The mode of determination used by Lygaeus
(milkweed/seed eating bugs) and most mammals.
• The presence of two X chromsomes (XX) in the zygote results
in female offspring (homogametous).
• The presence of one X chromsome and one Y chromosome
(XY) results in male offspring (heterogametous)
• All female gametes have an X chromosome, male gametes
have either X or Y.
BE ABLE TO DEFINE
• Sex determination by temperature
• For all crocodiles, most turtles, and some lizards, sex
determination is achieved according to the incubation
temperature of eggs during a critical period of embryonic
development
• Three different patterns of temperature sex determination in
reptiles is shown below.
SEX-DETERMINING SYSTEMS
BE ABLE TO DEFINE
• Klinefelter Syndrome
• A genetic disorder in human males caused by the presence of one or more extra X
chromosomes. Klinefelter males are usually XXY instead of XY. This syndrome often
includes enlarged breasts, small testes, sterility, and mild mental retardation.
• Persons with Klinefelter syndrome have:
•
•
Male genitalia (therefore have Y)
More than one X chromosome (usually XXY, or a 47, XXY karyotype, also can be XXXY or
XXXXY. 47,XXY
• Turner Syndrome
• A genetic disorder in human females caused by a 45,X genotype. Such individuals are
phenotypically female but are sterile because of undeveloped ovaries.
• Persons with Turner syndrome usually have (XO where O is absence of a chromosome):
•
•
•
A single X chromosome
No Y chromosome (45, X karyotype) 45,X
Female genitalia
• Such syndromes provide evidence that the Y chromosome determines maleness.
• Down Syndrome
• Results from trisomy of chromosome 21.
• Down syndrome has 12 to 14 characteristics, and affected individuals express 6 to 8 on
average.
• Down syndrome is usually a result of the nondisjunction of the maternal chromosome 12
during meiosis, only 5% of the time is it caused by the nondisjunction of the paternal
chromosome.
• Increased incidence with increasing maternal age.
• 47,XX,+21
BE ABLE TO DEFINE
• Familial Down Syndrome
• Heritiable down syndrome that runs in families.
• Involves a translocation of chromosome 21 with chromosome 14
• Example of Robertsonian translocation
• Patau Syndrome
• Results in trisomy of chromosome 13
• 47,XX+13
• Edwards Syndrome
• Results in trisomy of chromosome 18
• 47,XX,+18
• Cri-du-chat
• A clinical syndrome produced by a deletion of a portion of the
short arm of chromosome 5 in humans. Afflicted infants have a
distinctive cry that sounds like a cat.
• 46, 5pThe Academic Support Center @ Daytona State College (Science 102, Page 18 of 47)
BE ABLE TO DEFINE
• Y-pseudoautosomal regions (PARs)
• Present on both ends of the Y chromosome are the pseudoautosomal regions that
share homology with regions on the X chromosome and synapse and recombine with it
during meiosis.
• Y-SRY encodes TDF
• SRY (Sex Determining Region) has a gene that encodes for a protein called testisdetermining factor (TDF) that triggers testes formation.
• Barr bodies
• Densely staining DNA-positive mass seen in the somatic nuclei of mammalian females.
Discovered by Murray Barr, this body represents an inactivated X-chromosome.
• The inactive X is highly condensed, can be observed in stained interphase cells.
• Lyon hypothesis
• The proposal describing the random inactivation of the maternal or paternal X
chromosome in somatic cells of mammalian females early in development. All
daughter cells will have the same X chromosome inactivated as in the cell they
descended from, producing a mosiac pattern of expression of X chromosome genes.
• X-inactivation center (Xic)
• Is active on the inactive X chromosome.
• A region of the mammalian X chromosome that is the major control unit of inactivation.
Located on the proximal end of the p arm in human. Its genetic expression occurs only
on the X chromosome that is inactivated.
• It consists of the X-inactive specific transcript (XIST) gene which is critical for X
chromosome inactivation
• Two noncoding genes in Xic locus, Tsix and Xite play important roles in X chromosome
inactivation
BE ABLE TO DEFINE
• Aneuploidy
• Variations in chromosome number, when an organism gains or loses one or more
chromosomes and has other than an exact multiple of the haploid set.
• A condition in which the chromosome number is not an exact multiple of the haploid
set.
• Euploidy
• Complete haploid sets of chromosomes are present.
• Euploid – Polyploid with a chromosome number that is an exact multiple of basic
chromosome set.
• Haploid (n)
• A cell or organism having one member of each pair of homologous chromosomes.
Also refers to the gametic chromosome number.
• Diploid (2n)
• A condition in which each chromosome exists in pairs; having two of each
chromosome.
• Polyploidy
• Occurs when more than two sets of chromosomes are present. (extra complete sets of
chromosomes)
• Polyploid – A cell or individual having more than two haploid sets of chromosomes.
•
•
•
Triploid (3n) – Possessing three haploid sets of chromosomes.
Tetraploid (4n) – Possessing four haploid sets of chromosomes.
Pentaploid (5n) – Possessing five haploid sets of chromosomes.
BE ABLE TO DEFINE
• Allopolyploidy
• When polyploidy originates by the combination of chromosome sets from different
species as consequence of interspecific matings.
• Allopolyploid – polyploid condition formed by the union of two or more distinct
chromosome sets with a subsequent doubling of chromosome number.
• Autopolyploidy
• When polyploidy originates by the addition of one or more sets of chromosomes identical
to haploid complement of the same species.
• Polyploid condition resulting from the duplication of one diploid set of chromosomes.
• Endopolyploidy
•
•
•
The increase in chromosome sets with somatic nuclei that results from endomitotic replication.
The condition in which only certain cells in an otherwise diploid organism are polyploid.
In these cells, replication and segregation of chromosomes occur without nuclear division.
•
A cell division error in which homologous chromosomes (in meiosis) or the sister chromatids in
(mitosis) fail to separate and migrate to opposite poles; responsible for defects such as
monosomy and trisomy.
When chromosomes or chromatids fail to disjoin and move to opposite poles during meiosis I or II
• Nondisjuction
•
• Deletions
•
•
Missing regions of chromosomes.
When a chromosome breaks in one or more places and a portion is lost, the missing piece is
referred to as a deletion.
• Terminal deletion – deletion near end
• Intercalary deletion – deletion from the interior of the chromosome
BE ABLE TO DEFINE
• Duplications
• Repeated segments of genetic material
• Duplications arise as the result of unequal crossing over during meiosis or
through a replication error prior to meiosis.
• Inversions
• Inversion – a chromosomal aberration in which a chromosomal segment has
been reversed
• Translocations
• A movement of a chromosomal segment to a new location in the genome.
• Translocations alter the location of chromosomal segments in the genome
• Nonreciprocal translocations
• The transfer of genes from one chromosome to another nonhomologous
chromosome.
• Reciprocal translocations
• The exchange of segments between two nonhomologous chromosomes.
• Have unusual synapsis configuration during meiosis.
• Chromosome banding techniques
• Allow identification of the exact origin of the translocation and correlate the
presence of a chromosomal segment in hybrid cells with specific gene
expression. In this way, its possible to compile gene maps of human
chromosomes.
Be able to form a three gene map given percent
recombination between genes d-e; e-x, and d-x (not
alphabetical…plug in example percentages).
1) d-e
2) e-x
3) x-d
X
9%
20%
9%
D
E
1) a-b
2) b-c
3) a-c
30%
30%
50% (recall 50% is maximal recombination)
• (10 +10 ) / (10 +10 + 90 +90) = 10%
• Equations is
Recombinant / Total
Sum of two smaller numbers / Total
Be able to determine which product is on which
chromosome using synteny testing. Gene Product A is
on chromosome?
chromosome using synteny testing. Gene Product B is
on chromosome?
• Gene Product B is on chromosome 3
chromosome using synteny testing. Gene Product C is
on chromosome?
• Gene Product C is not on chromosomes 1 thru 7.
Although it could be on chromosome 8, there is not
enough information to prove that it is on
chromosome 8
chromosome using synteny testing. Gene Product D is
on chromosome?
Example of a XX/XY cross
• A red-green colorblind woman marries a man with
normal vision what are the genotypes and
phenotypes of the children?
Allele key
Xn = Normal Allele
Xb = Color blind Allele
Y = Y chromosome
Genotypes of
Woman - XbXb
Man - XnY
Xn
Y
Xb
XnXb
XbY
Xb
XnXb
XbY
• Genotypes - 2 XnXb : 2 XbY
• Phenotypes - 2 normal females : 2 color blind males
• In both genotype and phenotype the ratio reduces to 1:1
Example of a XX/XY cross
• A woman who is heterozygous for hemophilia marries
a man with hemophilia. What are the genotypes
and phenotypes of the children?
Allele key
Xn = Normal Allele
Xh = Hemophilia Allele
Y = Y chromosome
Genotypes of
Woman - XnXh
Man - XhY
Xh
Y
Xn
XnXh
XnY
Xh
XhXh
XhY
• Genotypes - 1 XnXh : 1 XhXh : 1 XnY : 1 XhY
• Phenotypes - 1 normal female : 1 hemophilic female:
1 normal male : 1 hemophilic male
Example of a ZW/ZZ cross
• In chickens, congenital baldness results from a Z-linked recessive
gene. A bald rooster is mated with a normal hen. The F1 from this
cross are interbred to produce the F2. Give the genotypes and
phenotypes, along with their expected proportions, among the F1
and F2 progeny.
Allele key
Zn = Normal Allele
Zb = Baldness Allele
W = W chromosome
Genotypes of P generation
Female - ZnW
Male – ZbZb
F1
Zb
Zb
F2
Zn
Zb
Zn
ZnZb
ZnZb
Zb
ZnZb
ZbZb
W
ZbW
ZbW
W
ZnW
ZbW
•
•
•
•
F1 Genotypes - 1 ZnZb : 1 ZbW (note ratio already reduced)
F1 Phenotypes - 1 normal male : 1 bald female
F2 Genotypes - 1 ZnZb : 1 ZbW : 1 ZbZb : 1 ZnW
F2 Phenotypes – 1 normal male : 1 bald female :
1 bald male : 1 normal female
EXAMPLE OF ZW/ZZ
Y - CHROMOSOME
PAR – Pseudoautosomal
regions that share
homology with regions on
X chromosome
SRY – encodes TDF for
testes formation
Euchromatin – gene
containing region
Heterochromatin – region
without genes.
MSY has three regions
• X-transposed region
• X-degenerative region
• Ampliconic region
CONCEPT QUESTIONS / DEFINITIONS
• Does recombination occur in mitosis or meiosis?
• Recombination occurs during crossing over of Meiosis I.
• What are the three growth phases of bacteria
• Lag phase, log phase (exponential growth), stationary phase
• Lederberg-Zinder Experiment
• Led to the discovery of phage transduction in bacteria.
• Dosage compensation.
• Prevents excessive expression of X-linked genes in humans
and other mammals.
• Balances the dose of X chromosome gene expression in
males and females.
THE LEDERBERG-ZINDER EXPERIMENT
CROSSWORD
CROSSWORD
CROSSWORD
CONCEPT QUESTIONS
• Polyploidy with all chromosome sets from the same
species.
• Autopolyploidy
• Polyploidy with all chromosome sets from the
different species
• Allopolyploidy
• When bacteria from F+ cell donates DNA to an Fcell it is called _______.
• Conjugation
• Having true (normal) set or number of
chromosomes.
• Euploidy
CONCEPT QUESTIONS
• Having three complete sets of chromosomes
• Triploid
• A person with one X chromosome (XO) is female
with a condition called ________ syndrome.
• Turner
• Organism that can not synthesize all organic
compounds from inorganic nutrients is called a ____.
• Auxotroph
• More than one X chromosome is condensed and
can be seen in interphase cells and is called a ____
body.
• Barr
CONCEPT QUESTIONS
• Small pieces of DNA taken up by living bacteria cell
and integrated stably into the bacteria genome.
• Transformation
• Extra copies of gene(s) in a chromosome due to
mistake in recombination
• Duplication
• More than two full sets of chromosomes.
• Polyploid
• ________ is a process when genes can be
transformed together
• Cotransformation
CONCEPT QUESTIONS
• Lost of one chromosome is called _______.
• Monosomy
• After fusing cells of two different species
chromosomes are lost until a ______ is formed.
• Synkaryon
• An Hfr cell has the F+ factor _____ into the bacteria
genome.
• Integrated
• Bacteriophages can be involved in moving genes
from one bacterium to another through a process
call ________.
• Transduction
CONCEPT QUESTIONS
• When gene(s) are lost from a chromosome.
• Deletion
• Organism that can synthesize all organic
compounds from inorganic nutrients is called a ____.
• Prototroph
• When two cells of different species are fused it
forms a _____?
• Heterokaryon
• Name of unit for one percent recombination.
• Centimorgan
CONCEPT QUESTIONS
• A partial diploid in bacteria which is result of F’ (F
prime) mated to F-.
• Merozygote
• Down syndrome for example.
• Trisomy
Questions
Prepared by
D. Leonard (Learning Specialist)
The Academic Support Center @ Daytona State College
http://www.daytonastate.edu/asc/ascsciencehandouts.html

GENETICS TEST II - Daytona State College

Transcription

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